It is a cylindrical container that receives feed water from the economizer in the natural circulation and multiple forced circulation boilers, connects the circulation loop, and delivers saturated steam to the superheater.

The drum body is made of high-quality thick steel plate, which is one of the heaviest parts in the boiler. The main function of the drum is to store water, to separate the steam and water, and to remove the brine and sludge in the boiler water during operation to avoid the boiler water containing high concentration of salt and impurities from entering the superheater and steam turbine with the steam.

These salts and impurities, such as scaling, salt accumulation and corrosion on the superheater tubes and steam turbine passages, will affect the economic and safe operation of the equipment.

The steam at the outlet of the boiler generally has a certain quality standard. The internal devices of the drum include steam-water separation and steam cleaning devices, water distribution pipes, sewage and dosing equipment, etc. The function of the steam-water separator is to separate the saturated steam and moisture from the water wall, and to minimize the small water droplets carried in the steam.

Baffles and gap baffles are commonly used as coarse separation elements in medium and low pressure boilers. In addition to the extensive use of various types of cyclone separators for coarse separation, boilers above medium pressure also use shutters, steel wire mesh or steam equalizing plates for further separation.

With the improvement of water treatment technology, steam separation devices tend to be simplified and finalized. The blowdown device (including continuous blowdown and regular blowdown) can discharge part of the boiler water containing higher salt and sludge during the operation of the boiler. The drum is also equipped with water level gauges, safety valves and other monitoring and protection facilities.